General Knowledge - Basic General Knowledge - Discussion


If speed of rotation of the earth increases, weight of the body

[A]. increases
[B]. remains unchanged
[C]. decreases
[D]. may decrease or increase

Answer: Option C


No answer description available for this question.

Priya Jain said: (Nov 27, 2010)  
Please explain the reason.

Arijit said: (Feb 21, 2011)  
What's the reason?

Aabhas said: (Apr 10, 2011)  
Gravity is relative to the reference frame. Einstein proved that acceleration and gravity are indistinguishable. If the reference frame is accelerating toward Earth's axis, then centrifugal acceleration of the reference frame partly cancels the gravitational attraction of Earth's mass.

It is ridiculous to make impossible assumptions; Earth's rotation will not increase significantly in less than a million years. However, at the equator, you weigh slightly more on a westbound train than on an eastbound train. In a sidereal reference frame centered on Earth but not rotating with Earth, your weight doesn't change.


Akshay said: (Aug 5, 2011)  
Hi every1,

I think in this case the question is about what effect will increased rotation have on the body on the surface of the earth.

The solution can be understood in a very simple example, if we are traveling in a car and it takes a left turn, we are pushed towards right, here the force acting is the centrifugal force which pushes the body outwards.

Similarly for a body on the surface of the earth, if the earth's rotation increases the centrifugal force will be acting on each body to throw it outward, but due to gravity it will not be thrown off.

And weight=mass* g(acc. due to gravity)

but in this case,

weight= mass* (g - the centrifugal force)

Hence the weight of the body would decrease when rotation increases..

Do let me know if any thing else is required in this regard.

Sudhakar said: (Feb 27, 2012)  
Excellent !

Rajan said: (Mar 28, 2012)  
Excellent Explanation Akshay..!

P R Patel said: (Mar 30, 2012)  
Good Explanation.

Sirisha said: (Apr 12, 2012)  
I have some doubt in Akshay's answer. If centrifugal force trying to pull the body outside then the centrifugal force on the body increases. Then why don't we add centrifugal force to the weight. And why do we need to add centrifugal force to weight.

Kaushal said: (May 24, 2012)  
Weight=m*g (in general case).

Now as the earth rotates with more speed it is likely to produce more centrifugal force as per mv^2/r as we (velocity) will increase as stated. Are (radius of earth) remains constant.

Now centrifugal force tries to cancel out the gravity force (basic concept). The increase in centrifugal force will try to decrease weight of body which is essentially nothing but gravity's effect on mass.

If you observe the same principle is used in satellites, as they rotate with certain speed they come under earth's gravitation field or in other words they cancel out gravitation force which is trying to bring satellite on the earth.

Prince said: (Sep 2, 2012)  
Weight shuold remain constant. Because being in inertial frame. No effect on body's weight should take place.

Happy said: (Sep 14, 2012)  
As we all know energy(E)=1/2MV^2 and weight=Mg

So from the first equation we can get M=2E/V^2. Then put this value in second equation, so now the result comes weight(W)=2E/gV^2. So,if V increases then W decreases.

Tushita said: (May 28, 2013)  
A little bit of physics will tell you that the speed of rotation of the earth has a direct effect on acceleration due to gravity.

And Acceleration due to gravity in turns affects the weight because weight=mass*acceleration due to gravity.

A simple equation gives us the relation between acceleration due to gravity and angular velocity of the earth which is g'=g-rw^2
Where g' = resultant acc due to gravity.
g = acc due to gravity on surface of the earth (= 9.8 m/s^2).
r = radius of the earth.
w(omega) = angular velocity of earth I.e. velocity at which earth is rotating about its axis.

This simply means that greater the w(omega) lesser would be g' and consequently lesser would be the weight.

Hope that makes things a little more clear.
P.S.The equation is derived in class 11 physics of any board.

Tushita said: (May 28, 2013)  
I'm sorry if that was too technical an explanation, I do realise this was a General knowledge question but that seemed like the most legit explanation.

Rajaraman said: (Nov 8, 2013)  
Dear Friends. This is all about the formula E= mc(square). Try to recall and calculate that. In short " when a body travels with the speed of light it gets converted into energy (in short mass or weight reduces) Clear?

Randomstudent said: (Dec 29, 2013)  
Force(centripetal force = mvr where m is the mass of the body and v is the velocity ie speed) remains same. So when v increased, m decreases.

Mr. Happy Love said: (Apr 23, 2015)  
Take a cosco ball and dip it in water. Take it out and slowly rotate it, and then rotate it fast, when you rotate it slow nothing will happen but when you rotate it fast water will sprinkle out.

Same is the case with earth if it starts rotating fast the objects on it will be pushed outside but the gravitational pull will hold them. Hence the weight will be reduced. :-).

Gauri Shankar said: (Oct 28, 2015)  
g' = g-w^2rcos^theta.

w = Angular velocity if w increases g' decreases.

Happy said: (Jan 6, 2016)  

Its centripetal force not centrifugal that makes a body to follow circular path.

Abdul Rahman said: (Jan 8, 2016)  
If spinning speed of earth decreased than weight of the body at poles does not change why?

Amrit said: (Mar 5, 2016)  
If the rotating speed of earth increase then our body weight will be decrease because by the acceleration of speed centrifugal force will produce which will reduce the gravity force.

V.Pooja said: (Jun 28, 2016)  
Good explanation. Thank you all.

Sumit said: (Sep 10, 2016)  
With rotational speed centrifugal force on us outward increases, decreasing the force on us due to gravity.

Repi said: (Oct 24, 2016)  
It's true I think it follows the newtons third law.

Nishan said: (Oct 25, 2016)  
The centripetal force also acts there towards the center. Why does the weight not increased?

Venkatesh said: (Nov 25, 2016)  

How can you add or subtract the centrifugal force from gravity? Please check the dimensions of both.

Sanap said: (Nov 26, 2016)  
If the rotation of earth increases, the weight of body decreases.

Then why the gravity or weight on Neptune is less?

Priyanshu said: (Aug 14, 2017)  
Mass of earth decreases as velocity increases so gravity also decreses.

Mahesh K said: (Aug 25, 2017)  
In W = Mass * Acceleration.

How does weight of the body would decreases, when rotation increases. The gravitational force also increases. As W & g. Directly proportional. So, please tell me how does weight of the body decreases?

Aaaaa said: (Nov 14, 2017)  
Awesome. I would like to know where the weight of body remains same on earth.

Hamza said: (Nov 20, 2017)  
Basically, it can be said that.

If the speed of rotation of earth increases so will the centrifugal force, which will try to nullify gravity.

Santhiswaroop said: (Jan 31, 2018)  
Good explanation @Akshay.

Prashanth King said: (May 15, 2018)  
Velocity increase mass decrease.

Anand said: (Jul 22, 2018)  

The centrifugal force is acting towards the centre of the earth not away from it. There is nothing to do with the centrifugal force. Its about the gravity changes, the value of the accl. Due to gravity decreases thus the weight decreases.

Ritesh said: (Dec 26, 2018)  
Mass of an object possessing kinetic energy is low compared to the body under rest.

Yugapooja said: (May 25, 2019)  
Thank you all for explaining this.

Ashrith said: (Jul 16, 2019)  
Good explanation, Thanks @Akshay.

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